A Sinusoidal Pulsewidth Modulation (SPWM) Technique for Capacitor Voltage Balancing of a Nested T-Type Four-Level Inverter

In this letter, a new control method based on the sinusoidal pulsewidth modulation scheme is proposed to control capacitor voltages of a T-type four-level nested neutral-point-clamped (NNPC) inverter. The T-type four-level NNPC inverter has a lower number of switches and components compared with other four-level classic and advanced inverters, which make this topology attractive for high-power medium-voltage applications. This topology has been proposed and studied with the assumption of constant dc sources instead of flying capacitors. In this letter, a simple single-phase modulator is developed to balance flying capacitor voltages. The performance and the feasibility of the proposed control technique are evaluated experimentally under a steady-state and transient conditions and for different modulation indexes and loads. The experimental results demonstrate the effectiveness of the developed control method to control the capacitors' voltages.